Drought and air pollution affect nitrogen cycling and free radical scavenging inPinus halepensis(Mill.)

Deciphering the ozone-induced changes in cellular processes: a prerequisite for ozone risk assessment at the tree and forest levels

“…The lack of any direct relation between species sensitivity and apoplastic Asc levels was attributed (i) to the high level of Asc oxidation in this compartment, (ii) to its low concentration relative to the total cell content and (iii) to the occurrence of other antioxidants (Castagna and Ranieri 2009;. At the whole-leaf level, changes in Asc content increased or decreased according to the exposure level and the duration of O 3 treatment, the leaf age, the growth stage or the position of the leaf in the canopy Strohm et al 2002;Tausz et al 2004;Wellburn et al 1996). Thus, the higher O 3 sensitivity of young beech in phytotrons compared to adult forest trees in the field has been partly attributed to differences in detoxification capacity and notably total ascorbate concentration (Nunn et al 2005).…”

“…Glutathione is known as an antioxidant, able to directly react with ROS, sometimes functioning in a compensatory manner to Asc but also with specific functions (Noctor et al 2012). Total glutathione and/or reduced glutathione content generally increased in leaves of tree species under O 3 fumigation (100 to 120 ppb) (Dumont et al 2014;Wellburn et al 1996). In adult beech trees, the glutathione level is affected by canopy position, but O 3 exposure (twofold ambient concentration) involved higher content in both shade and sun leaves (Herbinger et al 2005).…”

“…The protective effect of drought may be the result of stomatal exclusion of O 3 but also the induction of defence reactions (Matyssek et al 2006). Other works underlined that the combined effects of drought and O 3 could also decrease the antioxidant capacity of leaf cells in a higher extent than with the constraint alone, leading to a higher susceptibility to oxidative stress (Wellburn et al 1996). Thus, in these conditions of combined stresses, the fine-tuning between O 3 uptake and defence capacity appears crucial (Matyssek et al 2006).…”

Impacts of ozone on forests: a European perspective

“…Gorissen et al (1994) found no changes in starch concentrations in Douglas fir (Pseudotsuga menziesii) exposed to acute O $ concentrations. Wellburn et al (1996) report differences at the species level, for example between spruce and pine, in O $ effects on sucrose and raffinose concentrations. Effects vary with needle age, older needles showing lower sugar levels whereas younger needles can show elevated sugar concentrations because O $ has stimulated photosynthesis (Tingey, Wilhour & Strandley, 1976).…”

“…This increase, reversible at low but irreversible at higher O $ concentrations, is correlated with reduced membrane integrity and guard cell viability (McAinsh et al, 1996). Wellburn et al (1996), exposed droughted Aleppo pines to a single episode of O $ and found no interactive effects of O $ and drought on stomatal conductance, total C or N, N assimilation, protein, or nitrate reductase activity, although individually these stresses were important. Interactions associated with C assimilation, ascorbate and glutathione content and the amount of glutathione reductase protein were found, indicating that the ability to resist oxidative stress determines plant response to a combination of drought and O $ , very similar to the indications emerging from the free Ca# + and guard cell studies.…”